Today, we await an incoming missile. The University of
Houston's College of Engineering presents this series
about the machines that make our civilization run, and
the people whose ingenuity created them.

In 1908 a meteorite exploded over
Siberia's barely populated Tunguska River region with a
destructive force of 10 to 50 megatons of TNT. It
flattened forests and killed reindeer herds, but only a
few people died. It took years to diagnose what'd
happened. Once we knew, we shrugged it off as too rare to
worry about, even though that same explosion over a big
city could kill ten million people.

Now a disturbing incident comes to light. In 1930,
inhabitants along the Curuça River in
Western Brazil near Peru saw a blood-red sky and a rain
of red dust followed by an eerie whistling sound and
fireballs in the sky. Another meteorite in a remote
place! This explosion was only 1/10 as powerful as the
Tunguska explosion. Yet that's still 50 times as powerful
as the Hiroshima bomb.

A Jesuit missionary arrived five days later. He talked
with locals, who were still terribly alarmed. He told
their story, seven months after the fact, in a Vatican
newspaper.

We've only recently diagnosed the Curuça
event. It was probably a cluster of three meteorites.
That's why dust from the first impact was seen before the
other two landed.

There's a grim message here. We once thought the Tunguska
Meteorite was a once-in-300-years event. But
Curuça was only 22 years later. Within our
solar system, and just outside it, some ten trillion
meteorites, comets, and asteroids move in their shaky
orbits. Cosmic junk reaches us all the time.

The Tunguska meteor was 90 feet across. The meteorite
that we believe killed off the dinosaurs and 3/4 of
Earth's living creatures, 65 million years ago, had to've
been around 10 miles in diameter. That one completely
altered the Earth.

Today, astronomers are building complete records of
orbiting objects. By the year 2008, they hope to know
just what's headed our way. Then the question will be,
"How much warning do we have?" Five years is too little.
The closer the object is, the harder it'll be to deflect
its orbit. Fifty years warning should give us time to
launch an explosive device that could deflect a small
asteroid. Of course anything as little as the Tunguska or
Curuça meteorite will be very hard to locate
in time to intercept.

As a postcript to Curuça, It came to light in that
Jesuit priest's obituary that he reached the
Curuça River in the nick of time. The people
had seen the meteor as the wrath of their God and were
preparing to commit mass suicide. He talked them out of
it.

If that sounds silly, ask how you or I would react to a
piece of iron, large enough to exterminate us, headed
this way. Somewhere out there, there is one. We have to
be cool-headed problem-solvers today, if we don't want to
face that inexorable force of nature -- without the means
for averting it.

I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.